The Press Association said key factors in the panel’s decision would include the inability of Mr Assange to access political asylum, the fact he has never been charged, and changes to UK law and procedures since he arrived at the embassy.

Wikileaks earlier tweeted it was waiting for “official confirmation” of the UN panel’s decision.

Downing Street said the panel’s ruling would not be legally binding in the UK while a European Arrest Warrant remained in place.

“We have been consistently clear that Mr Assange has never been arbitrarily detained by the UK but is, in fact, voluntarily avoiding lawful arrest by choosing to remain in the Ecuadorean embassy,” a spokesman said.

“The UK continues to have a legal obligation to extradite Mr Assange to Sweden.”

The Swedish foreign ministry said in a statement that it noted the UN panel’s decision “differs from that of the Swedish authorities”.

The statement added the legal process for Mr Assange’s case would be handled in court by Swedish prosecutors.

Image captionMr Assange issued his statement on Twitter

Per Samuelsson, Mr Assange’s lawyer, said Swedish authorities would be “morally” wrong to continue the investigation if the UN panel found in his favour.

“The ball is in Sweden’s yard, in the prosecutor’s yard. She is not formally bound by the decision by the UN, but morally it is very difficult to go against it.”

The journalist John Pilger, who is a friend of Mr Assange, said “the ball is now at the feet of the British government”, whose international legal “obligations” were represented by the UN panel.

“They did something in terms of supporting the tribunal in all the other celebrated cases, and Assange now joins them because the UN jurists have clearly found this is a case of arbitrary detention,” he said.

Media captionAssange’s supporter and friend Vaughan Smith hopes he will now be freed

Mr Assange’s Wikileaks organisation posted secret American government documents on the internet, and he says Washington could seek his extradition to the US to face espionage charges if he is sent to Sweden.

In the statement, published earlier by Wikileaks on Twitter, Mr Assange said: “Should the UN announce tomorrow that I have lost my case against the United Kingdom and Sweden I shall exit the embassy at noon on Friday to accept arrest by British police as there is no meaningful prospect of further appeal.

“However, should I prevail and the state parties be found to have acted unlawfully, I expect the immediate return of my passport and the termination of further attempts to arrest me.”

Last October, Scotland Yard said it would no longer station officers outside the Ecuador embassy following an operation which it said had cost £12.6m. But it said “a number of overt and covert tactics to arrest him” would still be deployed.